(1) Field of the Invention
This invention relates to a light or radiation detecting unit manufacturing method, and a light or radiation detecting unit manufactured by this method, for use in the medical field, industrial field, nuclear field and so on.
(2) Description of the Related Art
An imaging apparatus that obtains images based on detected light or radiation has a light or radiation detector for detecting light or radiation. Such a detector will be described, taking an X-ray detector for example. An X-ray detector has an X-ray converting layer (semiconductor layer) of the X-ray sensitive type. The X-ray converting layer converts incident X-rays into carriers (charge information). The detector detects the X-rays by reading the carriers. Amorphous selenium (a-Se) film, for example, is used as the X-ray converting layer (W. Zhao, et al., “A flat panel detector for digital radiology using active matrix readout of amorphous selenium”, Proc. SPIE Vol. 2708, pp. 523-531, 1996).
In a radiographic operation carried out by irradiating an object under examination with X-rays, radiographic images transmitted through the object under examination are projected onto the amorphous selenium film, thereby generating carriers proportional to the densities of the images in the film. The carriers generated in the film are collected by carrier collecting electrodes in a two-dimensional arrangement. After the collection is continued for a predetermined time (called “accumulation time”), the carriers are read outside via thin-film transistors.
For manufacturing such an X-ray detector, amorphous selenium film is formed by vapor deposition on a glass substrate (insulating substrate) having a pattern formation of switching elements consisting of thin-film transistors and the above carrier collecting electrodes arranged two-dimensionally (S. Adachi, et al., “Experimental Evaluation of a-Se and CdTe Flat-Panel X-ray Detector for Digital Radiology and Fluoroscopy”, Proc. SPIE Vol. 3977, pp. 38-47, 2000).
A technique has been proposed for forming a pattern of thin-film transistors on a glass substrate by vapor deposition or printing (ink jet method, or a kind of stamping or coating method) of organic molecules (““Organic Transistors and Printable Integrated Circuits”—Nanoelectronics”, [online], Internet <URL: http://www.nanoelectronics.jp/kaitai/printableofet/2.htm>). Organic low molecules, typically single crystals such as pentacene and naphthacene, among organic molecules are suited for formation by vapor deposition. Organic polymers are suited for formation by printing method.
Such an X-ray detector has peripheral circuits such as an amplifier array circuit for amplifying the carriers detected by the detector, and an analog-to-digital converter for converting the amplified carriers from analog values to digital values. These components are contained in a case (storage container) in order to combine them into a unit as disclosed in Japanese Patent No. 3577003. An X-ray detecting unit formed in this way serves as a portable type capable of being carried about conveniently.
The gross weight of the portable detecting unit should be 4 to 5 kg or less to meet the condition that the unit can be carried in one hand. However, as noted above, the conventional construction has thin-film transistors formed as a pattern on a glass substrate. Therefore, to realize a size for imaging the human chest (e.g. a size 43 cm×43 cm), for example, the weight of the glass substrate alone would account for about 1 kg.
A large glass substrate breaks very easily, and scrupulous care must be taken not to apply a shock in time of transport and use. This imposes great restrictions, for example, when the detecting unit is used outdoors such as at a disaster site, or when the detecting unit is carried and used in a medical checkup vehicle.